This invention relates to solid fuel burning stove and in particular to stoves of the above type that burn solid fuels which develop smoke with a high soot content as a result of incomplete combustion. An example of the foregoing is a wood burning stove.
Stoves of the above type have as desirable features complete combustion of fuel even at low temperatures, after-burning of the primary combustion gases and means to provide a soot free transparent viewing window (if a window is fitted) so that the owners of the stove can watch the fuel burning process. Attempts have been made to provide stoves having all of the above features, however in the area of maintaining substantially complete combustion for a range of combustion air intakes difficulties have arisen, largely because of the controls that have been used for the combustion cycle.
In general, stoves for burning solid fuels comprise a combustion chamber with a draft generating flue provided with a damper to regulate the drawing ability of the flue and an air inlet with a flow control operable between a fully open condition (designed to provide sufficient combustion air to allow the stove to perform up to the maximum designed level) and a fully closed condition. In most stoves reliance is put upon leakage of air into the combustion chamber to maintain a slow combustion rate when the air inlet is closed off. This makes the operation of the stove easy for the user because if slow combustion is required then it is simply a matter of closing off the air inlet completely and relying on the air leakage into the combustion chamber to sustain combustion. The problem is that the amount of air leaked into the combustion chamber depends on many factors and can vary substantially from stove to stove of the same make and therefore efficient combustion in the slow combustion mode of operation cannot be guaranteed. If incomplete combustion occurs where wood is the fuel smoke and creosote can be generated. If this continues there will be a build up of soot in the flue from the combustion chamber and on the inner surface of the combustion chamber, including the viewing window if one is fitted. It is known that if a stream of air is directed across the inner face of a viewing window of a combustion chamber the window will be maintained substantially clear of soot irrespective of the rate of combustion occuring in the combustion chamber.
One aspect of the present invention is the provision of a permanent supply of combustion air to the combustion chamber which is sufficient to maintain substantially complete, but slow, combustion when the combustion air control means is in the appropriate position. The invention also provides an air supply which is directed so as to inhibit the deposition of any soot which results from the combustion process on the inner surface of the viewing panel provided in the stove. A further feature of the invention is a catalytic means to ensure ignition of the products of primary combustion in a secondary combustion zone of the combustion chamber.